This invention relates to a treatment system for alkaline or acid solutions containing heavy metals, and more particularly, it relates to a system and method for substantially neutralizing a low or high pH solution and removing heavy metals therefrom.
Systems and methods for neutralizing aqueous solutions and removing contaminants therefrom are well known in the prior art. For example, CO.sub.2 gas is injected into alkaline solutions to lower the pH of the solution. However, a problem that is prevalent in many of these systems is the large equipment required for performing such steps. The equipment can include, for example, large holding and mixing tanks, large settling tanks and clarifiers. Further to the use of such large equipment, large amounts of chemicals have to be added for purposes of neutralization or flocculation, and this also can lead to disposal problems.
In the art, U.S. Pat. No. 4,188,272 discloses treatment of an aqueous solution containing hexavalent chromium by electrolytic addition of ions to form metal hydroxides in a stream at pH of 4.5 to 5.8. U.S. Pat. No. 4,693,798 discloses electrolytically generating Fe ions in a solution having a pH of less than 2.8 and containing hexavalent chromium to form metal hydroxides, thereby removing the hexavalent chromium. U.S. Pat. No. 4,163,716 discloses the use of electrolysis with an iron cathode to form ferric and ferrous hydroxide to remove heavy metal ions and colored substances after ion exchange of a dye house effluent. U.S. Pat. No. 5,013,453 discloses a method for removing heavy metal ions from an aqueous solution wherein the method comprises coprecipitating heavy metal ions with a carrier precipitate which is formed in situ.
Thus, there is a great need for a compact and efficient system for neutralizing a high pH solution, for example, and for removing heavy metals therefrom prior to disposing of the solution. The present invention provides such a system which enables reduction of pH from 11 or 12, for example, to about pH of 7 and at the same time enables removal of heavy metals such as chromium ions, etc., from such solution. For example, with respect to heavy metals, the present invention enables reduction of chromium to a level of 0.02 ppm. Further, as well as treating basic or alkaline solutions, the invention is capable of neutralizing acidic solutions and removing heavy metals therefrom.